Write a program to covert Toggle characters.

#include<conio.h>
#include<stdio.h>
int main()
{
FILE *fp;
char ch;
fp=fopen("e:\\abc.txt","r");
if(fp==NULL)
printf("error to open");
while(1)
{
ch=fgetc(fp);
if(ch>='A' && ch<='Z')
{
ch=ch+32;
printf("%c",ch);
}
else if(ch>='a' && ch<='z')
{
ch=ch-32;
printf("%c",ch);
}
if(ch==EOF)
break;
}
fclose(fp);
}